Relative phase (a quantification of the relative timing between a pair of oscillators at the same frequency) has been used extensively in the able-bodied (AB) population to measure motor control (Collins et al., 1998), but never in cerebral palsy (CP). The purposes of this pilot investigation are to develop relative phase as a measure of motor control at the ankle for persons with CP, and relate the motor control measure to spasticity, strength, and function. Aim 1 is to develop a measure of motor control for the ankle dorsi/plantarflexors in persons with CP. Fifteen subjects with CP (CP group) and 15 with able bodies (AB group) will perform three movement tasks (1) move one (then the other) ankle to maximum dorsiplantarflexion in time with a pair of metronome beeps, (2) synchronize (i.e., in phase) their ankle movements, and (3) dorsiflex one ankle while plantarflexing the other and vice versa (i.e., antiphase). The tasks will be recorded using a motion capture system. Relative phase will be calculated between the ankle and the metronome or between the ankles. A mixed-design ANOVA will be used on the standard deviation of the relative phase measures to determine if differences exist between the CP and AB groups, and between tasks. The variability in the three relative phase tasks is expected to be less for the AB group compared to the CP group. It is hypothesized that the group differences will increase with task difficulty. Aim 2 will correlate the motor control measure with spasticity, strength, and function. The motor control measure from Aim 1 will be used with other tests to assess additional CP and AB groups (n=12 subjects/group). Subjects will be tested for motor control, spasticity, and strength, gait, gross motor function measure [GMFM]. Multiple regression will quantify relationships among the measures. The PIs hypothesize that the motor control measure will add to the amount of function variability explained by spasticity and strength. Upon completion, they will have data to initiate a more extensive study to quantify relationships between impairment measures and function.